Polymorphonuclear leukocytes (PMNs) act as 'first-responders' to microbial infections in the human gingiva. Microbial clearance by PMNs, however, is inhibited by the plaque biofilm. PMNs undergo apoptosis, and may progress to a necrotic state causing collateral damage to surrounding tissues, eventually exacerbating periodontitis. These effete PMNs are, in turn, cleared by antigen presenting cells such as macrophages and via largely unknown mechanisms by dendritic cells (DCs). The DC-PMN interaction may also contribute to DC maturation and regulate the cytokine profile, contributing to long term immunity or chronic inflammation. The outcome of DC-PMN interaction may depend to a large extent on the type of pathogen encountered. Porphyromonas gingivalis resists phagocytosis by PMNs. but is readily taken up by DCs, resulting in an immunosuppressive DC response. The aim of the training grant proposal is to establish the interactions of human DCs with PMNs and how oral pathogens alter these interactions in vitro. My hypothesis is that DCs and PMNs play a mutually cooperative role in resolution of inflammation and in immunity to oral pathogens such as P.gingivalis and that this role is dependent on several factors such as DC-PMN conjugate formation, the activation, apoptotic/necrotic state of the PMNs and DCs and the presence of infection with oral pathogens. These studies will be carried out initially with immortalized cell lines as proxies for DCs and PMNs, to establish the assays and to identify the most likely receptors involved in DC-PMN conjugate formation. This will be followed by use of monocyte-derived DCs and primary isolated PMNs. The formation of DC-PMN conjugates, uptake of PMNs by DCs, and DC expression of costimulatory molecules and secretion of Th-polarizing cytokines IL-12p70, IL-23, IL-6, IL-10, and IL-4 will be quantitated. DC will then be exposed to wild- type P. gingivalis, as well as minor, major fimbriated or non fimbriated strains to determine the influence of the DC-SIGN -targeting minor fimbriae on DC-PMN interactions. In general, it is expected that DC- PMN interactions may be mediated by the glycosylated ligands MAC-1 and CEACAM1 on PMNs and by C-type lectin DC-SIGN on DCs, thus causing cell clustering. However, DC-SIGN-Mac1/CEACAM interaction may not be sufficient for optimum uptake of PMNs by DCs; other co-receptors such as MR (CD206) and LFA-1 (CD11a/CD18) may be involved. Understanding the nature of these reactions between DCs and PMNs to P. gingivalis may lead to the detailed insight required for more effective means of treating chronic periodontitis.